1. Field of the Invention
The present invention relates to optical fiber cables and, more particularly, to an improved geometric arrangement of elements forming an optical fiber cable that decreases the diameter, linear weight and cost of the optical fiber cable while, at the same time, improving its mechanical performance.
2. Description of Related Art
With reference to FIG. 1, a prior art optical fiber cable assembly 2 includes a plurality of fiber optic tubes 4 and a plurality of adjacent wires 6 which provide some support to the cable design. A plurality of grounding members 8 surround tubes 4 and wires 6. When viewed from an end of optical fiber cable assembly 2, tubes 4 and wires 6 are received within an imaginary tube 10 which extends along the length of fiber optic cable assembly 2. Preferably, one wire 6 is positioned centrally within imaginary tube 10. This centrally positioned wire 6 is surrounded by tubes 4 and, if desired, other wires 6. The positions of tubes 4 and wires 6 around the centrally positioned wire 6 are determined based on the number of optical fibers 12 comprising optical fiber cable assembly 2. In the illustrated embodiment, a few optical fibers 12 are shown received within one of tubes 4. Preferably, however, each tube 4 is substantially filled with optical fibers 12.
In an exemplary embodiment of optical fiber cable assembly 2, tubes 4 and wires 6 surrounding the centrally positioned wire 6 have the same diameter and central wire 6 typically has a slightly larger diameter. The diameters of the various wires 6 and tubes 4 are selected so that each wire 6 and each tube 4 is tangent to any adjacent tubes 4 and/or wires 6. Similarly, each ground member 8 has a diameter that is selected so that each ground member 8 is tangent to its adjacent ground members 8. In practice, however, due to minor manufacturing variations in the diameters of grounding members 8, wires 6 and/or tubes 4, one or more grounding members 8 may not be tangent with their adjacent grounding members 8, and tubes 4 and wires 6 may not be tangent with their adjacent tubes 4 and/or wires 6.
Preferably, along the length of optical fiber cable assembly 2, tubes 4 and wires 6 are spiral wound in a first direction and grounding members 8 are spiral wound in a second direction, opposite the first direction. Subject to minor manufacturing variations, grounding members 8 are essentially tangent to an imaginary tube 10, which surrounds tubes 4 and wires 6 and which extends along the length of optical fiber cable assembly 2, and an imaginary tube 14, which surrounds grounding members 8 and which extends along the length of optical fiber cable assembly 2.
One problem with designs of optical fiber cable assemblies, like optical fiber cable assembly 2, is that the selection of wires 6 having the same, or nearly the same, outside diameter as tubes 4 increases the diameter and linear weight of optical fiber cable assembly 2. In addition, the number of tubes 4 comprising optical fiber cable assembly 2 will determine the number of wires 6 that can be utilized while maintaining the same geometric arrangement shown in FIG. 1. For example, in the geometric arrangement of optical fiber cable assembly 2 shown in FIG. 1, the sum of tubes 4 and wires 6 equals seven. Hence, the possible combination of tubes/wires is 1/6, 2/5, 3/4, 4/3, 5/2 and 6/1. As can be seen, the number of wires 6 decreases as the number of tubes 4 increases, and vice versa. Optical fiber cable assembly 2 is designed for aerial installation between utility poles or towers. As a result, in addition to supporting its own weight (self loading), optical fiber cable assembly 2 must also be designed to withstand weather related mechanical loads, such as wind loads, ice loads and snow loads, as well as electrical loads, such as short-circuits and lightning charges. Hence, decreasing the number of wires 6 while simultaneously increasing the number of tubes 4 is contrary to the need to increase the capacity of optical fiber cable assembly 2 to withstand weather related mechanical loads and electrical loads by increasing the number of wires 6 when the number of tubes 4 increases.
In addition, because of the geometric arrangement of tubes 4, wires 6 and grounding members 8 shown in FIG. 1, optical fiber cable assembly 2 has an outside diameter defined by imaginary tube 14. As would be appreciated by one of ordinary skill in the art, the diameter of imaginary tube 14 affects the possible weather related mechanical loads that could be experienced by optical fiber cable assembly 2 and related support structures. Namely, increasing the outside diameter of imaginary tube 14 increases the possible weather related mechanical loads that could be experienced by optical fiber cable assembly 2 and related support structures. In contrast, decreasing the outside diameter of imaginary tube 14 decreases the possible weather related mechanical loads that could be experienced by optical fiber cable assembly 2 and related support structures. Accordingly, in the design of optical fiber cable assemblies it is desirable to minimize the outside diameter while simultaneously maintaining or increasing the number of tubes 4 while, at the same time, providing a sufficient number of wires 6 of sufficient capacity to withstand expected self loading, possible weather related mechanical loads and electrical loads thereon when optical fiber cable assembly 2 is being installed and is in use. However, the geometric arrangement of tubes 4, wires 6 and grounding members 8 forming current optical fiber cable assemblies does not provide such an optimum design.
It is, therefore, an object of the present invention to overcome the above problems and others by providing a new optical fiber cable assembly that has an improved geometric design with improved mechanical and electrical performance over the prior art fiber optic cable assemblies. This improved geometric design enables the same number of optical fibers to be received in a smaller diameter than a prior art optical fiber cable assembly. In addition, the improved geometric design of the new fiber optic cable assembly enables the use of smaller diameter wires and grounding members while maintaining an amount of self loading, weather loading and electrical loading capacity that is commensurate with the smaller outside diameter and lower linear weight of the new fiber optic cable assembly. Still other objects will become apparent to those of ordinary skill in the art upon reading and understanding the following detailed description.